Abstract
In open channel flow, a secondary flow can be generated using a strip roughness that is at an angle to the direction of flow. In this study, we investigated the influence of the oblique angle of installation of the roughness elements on the secondary flow generation experimentally by the PIV method. A clear secondary current was formed due to oblique sharpness, which flows upwards at the near wall region and downward at the middle of the channel in the lateral direction, but the strength and structure of each of the components of the secondary currents varied depending on the installation angle. In the vicinity of the bottom surface, the flow velocity in the lateral direction (V) is remarkably weak in the case of the installation angle of 30°, and in the case of 45° and 60°, the flow velocity becomes almost equally large. On the other hand, the vertical flow (W) at the near wall region is noticeably strong in the case of installation angle of 60° and becomes weak and weaker in magnitude in the case of installation angle 45° and 30° respectively. Furthermore, the downflow at the middle of the channel is weak in the case of installation angle of 60° and increase in magnitude in the case of 45° and attains peak in the case of 30°.
